This invention relates to an apparatus to supply a highly-pressurized fluid medium to a machine element while rotating at a high speed, e.g., 1000 RPM's, from a stationary supply source of pressurized fluid medium. While not so limited, the apparatus of the present invention is particularly useful to supply hydraulic fluid under pressure to an expandable reel used to coil or uncoil metal strip incident to processing in a rolling mill. A piston and cylinder assembly is used to form an actuator in a tension or payoff reel for expanding and collapsing segments of an expandable mandrel. Sometimes in the past, a piston and cylinder assembly used to expand and collapse the segments of an expandable mandrel was connected to the mandrel in a manner such that the piston rotated on the cylinder wall while at the same time a pressurized fluid medium is applied to the piston, causing it to reciprocate along the cylinder wall to expand and collapse the segments of the mandrel. At a high speed of rotation by the mandrel, excessive amounts of heat and wear take place between the piston and the wall of the cylinder. To alleviate this problem, it has been proposed to arrange the piston and cylinder assembly for expanding the segments of the mandrel in a manner such that the entire piston and cylinder assembly rotates with the mandrel. It is necessary to couple the rotating piston and cylinder assembly to a controlled supply of pressurized hydraulic fluid medium from a stationary source. The necessary pressure of the fluid medium to expand the segments of the mandrel is substantial; normally about 1500 psi, but selected according to the design and intended use of the reel.
Mechanical seals that rub on the rotating and/or stationary parts in a device to control the flow of fluid medium between these parts are undesirable to conduct a pressurized fluid medium to a rotating machine element, such as the aforesaid piston and cylinder assembly for a reel. The rubbing action of the seal surfaces generates subtantial amounts of heat that distort these surfaces, particularly at high rotational speeds, e.g., 1000 RPM's or greater. Moreover, the design of the seal must perform in an adverse environment and must be effective against a high working pressure fluid of, for example, 1500 psi.